According to Wiktionary it's /fʁɑ̃.sɛ/. So like the English word "set" without the -t. Even including an "n" is not correct; it nasalizes the vowel. This is why English-like transcriptions can only take you so far. There's only so many sounds in English, and when languages start using ones that don't exist, it's impossible to bridge that gap.

As a monolingual English speaker until college, I have had a terrible time with distinguishing some word-final diphthongs. For instance, I catch myself using the English "-o" /oʊ/ in Spanish, when it should be just /o/. I also have a hard time with /e/ vs /eɪ/.

The point of using a simple respelling is to show it is not pronounced "Fran Kice". Anything better than that is an improvement.

"say" and "seh" sound pretty much the same to me, but I'm not a monolingual English speaker, I grew up in Germany and the US, and I might also mix up things.

I find the first syllable harder to describe, since there is no way to note these nasal sounds in English (actually, I think they should be called anti-nasal, since no air goes through the nose when I say it, but I disgress). But I think in general, some basics of French pronunciation are known to most English speakers, so using a French word is a bad example.

Are you making 'seh' rhyme with 'meh', or mostly with 'say', but saying it's subtly different? (If only there were some sort of phonetic alphabet eh...)

I would say it's most like the long 'a' in 'fate' or 'mate'.

I did mean rhyming with "meh", not a long "a" at all! In IPA, I'd say it's ɛ, like the vowel in the English word "bed".

So it really sounds like "a" to you? Huh.

Oh, interesting.

It does, yes, but as I alluded to that differs from 'ay' in which I'd linger slightly more on the end 'y' note if you see what I mean.

Less extreme than the way Americans linger on a syllable-ending 'r', but the same sort of thing.

IIRC that vowel is /e/, which is neither really /ɛ/ ('eh') nor the diphthong /eɪ/ ('ey'). And that quite neatly illustrates the problem with shoehorning other languages into English phonology and spelling.